Phenol is a useful chemical compound employed in the manufacture of a wide variety of substances, such as aspirin, oil of wintergreen and plastics. The oxidation of cumene to cumene hydroperoxide is the first step in an important commercial phenol synthesis. Therefore any means for increasing the rate of oxidation of cumene to cumene hydroperoxide would be of considerable commercial interest due to the added phenol production one might achieve without the need for new capital investment.
In this regard, many compounds have been claimed to improve the rate and/or selectivity of the cumene oxidation. As examples of such compounds one can cite a host of substances such as calcium carbonate, amines, and carbonyl compounds. There are also reports that certain salts may be catalytically active in this reaction including amine salts, certain 'onium tetrafluoborates and triphenylsulfonium chloride. In many instances experimental details are not available concerning the use of these compounds. Generally, however, the use of from 1000 ppm to 10,000 ppm of catalyst has been required.
Such large amounts of catalyst are costly primarily due to the lost efficiency which results when unwanted reaction products are formed along with the cumene hydroperoxide. Much effort has been expended to discover a catalyst which can be used in much smaller concentration to oxidize cumene. One such catalyst, triphenylsulfonium chloride, has shown effective catalytic activity in concentrations of as low as 50 ppm. However the efficiency of the triphenylsulfonium chloride catalyzed reaction has remained poor.
The oxidation of cumene to cumene hydroperoxide, like many free radical reactions, is quite sensitive to the presence of foreign material. The accidental contamination of cumene by phenol in concentrations as low as 150 ppm leads to a severe decline in the rate of oxidation of cumene to cumene hydroperoxide. Consequently, a preliminary costly purification of the phenol contaminated cumene is usually carried out. A means of eliminating the purification step, overcoming the decrease in oxidation rate which results from the contamination of cumene by phenol, and of increasing the oxidation rate without such a large sacrifice of efficiency would be highly desirable.